The disclosure generally relates to an LED control device and, more particularly, to the LED control device utilized in the phase-cut dimming system.
The LEDs (light emitting diodes) have the advantages of high luminous efficacy, long product life, compact dimensions, fast startup time, high reliability, high durability, etc. More and more people have replaced the traditional light sources with LEDs in the indoor and the outdoor environment, e.g., the house, the office, the billboard and the streetlamps.
The LEDs, however, may malfunction when cooperating with traditional circuits or control devices. For example, many traditional light sources may cooperate with the phase-cut dimming circuit for adjusting the brightness of the light sources. The phase-cut dimming circuit may comprise the TRIAC (triode for alternating current), the diode or other suitable circuit elements for cutting off part of the AC input signal so that the brightness of the light sources may be adjusted accordingly. When the AC input signal is cut off, the voltage or the current of the AC input signal is configured to be zero or a small value. In this field, the conduction angle is known as 180 degrees minus the angle corresponding to the cut-off portion of the AC input signal. For example, when the AC input signal is not cut off at all, the conduction angle is 180 degrees. When the AC input signal is completely cut off, the conduction angle is 0 degree.
Moreover, the LED control device is needed to drive the LEDs, stabilize the voltage, stabilize the current, adjust the power factor, etc. The LED control device, however, causes problems when adjusting the brightness of the LED in the phase-cut dimming system. For example, when the phase-cut portion of the AC input signal is too small (i.e., the conduction angle is large), the LED control device will perform the compensation operation to stabilize the voltage and/or the current. When the conduction angle is large, the voltage and/or the current supplied to the LED almost do not vary because of the compensation operations of the LED control device, and the brightness of the LED cannot be adjusted. Therefore, when the conduction angle is large, the dimming function cannot be performed correctly. The dimming linearity of the LED dimming system is affected, and the user cannot easily adjust the LED to the desired brightness.
Moreover, there are also other problems when the phase-cut dimmer cooperates with the LED to perform the dimming function. For example, when the AC input signal is phase-cut, the LED control device is not powered. Afterward, when the AC input signal is no longer phase-cut, some circuits in the LED control device will be restarted. In the period of restarting the circuits, the voltage and/or the current supplied to the LED usually differ from the value(s) before the AC input signal is phase-cut. Therefore, the dimming linearity of the LED dimming system is also affected, and the LED may even flicker. The users would notice and feel uncomfortable when the LED flickers in the phase-cut dimming system.